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PHP RFC: json_validate
- Version: 0.9
- Date: 2022-08-14
- Author: Juan Carlos Morales, dev.juan.morales@gmail.com
- Status: Under Discussion
- First Published at: http://wiki.php.net/rfc/json_validate
- Implementation: https://github.com/php/php-src/pull/9399
Introduction
This RFC introduces a new function called json_validate() to validate if an string contains a valid json.
Most userland implementations use json_decode() which by design generates a ZVAL(object/array/etc.) while parsing the string, ergo using memory and processing that could be save.
Proposal
Description
json_validate(string $json, int $depth = 512, int $flags = 0): bool
Parameters
json
The json string being analyzed.
This function only works with UTF-8 encoded strings.
Note:
PHP implements a superset of JSON as specified in the original » RFC 7159.
depth
Maximum nesting depth of the structure being decoded.
flags
Bitmask of JSON_INVALID_UTF8_IGNORE. The behavior of this constant is described on the JSON constants page.
Return values
Returns true if the string passed contains a valid json, otherwise returns false.
Examples
1. Validate a valid json-string
var_dump(json_validate('{ "test": { "foo": "bar" } }'));
Result will be
bool(true)
2. Validate an invalid json-string
var_dump(json_validate('{ "": "": "" } }'));
Result will be
bool(false)
Errors during validation can be fetch by using json_last_error() and/or json_last_error_msg().
Reasons to have json_validate() function in the core
Disadvantages of using json_decode to only validate a json-string
By design, json_decode() generates a ZVAL (object/array/etc.) while parsing the string, ergo using memory and processing for it, that is not needed if the only thing to discover is if a string contains a valid json or not.
Disadvantages of using regex
Using a regex for this task forces different, error-prone, hard to maintain, implementations.
Disadvantages of userland solutions
- Writing a JSON parser is no trivial
- They need to be up-to-date with the existing PHP JSON parser used by json_decode() already, otherwise a json-string valid in json_validate() might not be valid json-string for json_decode() or vice-versa.
- We already have a JSON parser in PHP, that is used by json_decode(); reusing the existing JSON Parser provides 100% compatibility between the validation of a json-string, and json_decode().
Needs from major projects and developers
In the “References” section, there is a list of major open-source php projects that could benefit with this new function.
Also in the mentioned section a link to one of the most popular StackOverflow questions is provided, which somehow reflects the need from our developers to have a feature like this included.
Please check the “References” section.
Complexity added in the core
At the moment, there is a JSON parser in the core, used by json_decode to do its job, so there is no need to write a new JSON parser for this RFC; the proposed function will use the existing JSON parser exclusively to parse an string without generating any object/array/etc. in memory for it.
Reasons NOT to have json_validate() function in the core
One member of the mailing list expressed that:
- Incorporating such a small implementation that can be achieve with
userland code is not a good idea.
Quote:
“If we keep the tendency to pollute already bloated standard library with an army of small functions that could have not exists and be replaced with normal PHP counterparts IMHO we'll end with frustration from developers as I believe DX slowly falls down here.”
- json_validate() would only be useful for edge cases.
Quote:
“A `json_decode()` is a substitute that IMO solves 99% of use cases. If I'd follow your logic and accept every small addition that handles 1% of use cases, somebody will raise another RFC for simplexml_validate_string or yaml_validate and the next PhpToken::validate. All above can be valid if we trust that people normally validate 300MB payloads to do nothing if they DON'T fail and there is nothing strange about that.”
- The user also provided an implementation of a JSON parser written in pure PHP. https://gist.github.com/brzuchal/37e888d9b13937891c3e05fead5042bc
Backward Incompatible Changes
None, as this is a new function only.
json_validate will no longer be available as a function name.
Proposed PHP Version(s)
next PHP 8.x
RFC Impact
This RFC has no impact on SAPIs, existing extensions, Opcache, etc.
Open Issues
- No open issues
Future Scope
- (To be defined by future discussions if needed)
Proposed Voting Choices
- (To be defined)
Implementation
- Github: https://github.com/php/php-src/pull/9399
References
Major Open-Source projects that will benefit out of this
class JsonValidator extends ConstraintValidator
public function validateJson($attribute, $value) { if (is_array($value)) { return false; } if (! is_scalar($value) && ! is_null($value) && ! method_exists($value, '__toString')) { return false; } json_decode($value); return json_last_error() === JSON_ERROR_NONE; }
public static function isJson($value) {
protected function isValidJsonValue($value) { if (in_array($value, ['null', 'false', '0', '""', '[]']) || (json_decode($value) !== null && json_last_error() === JSON_ERROR_NONE) ) { return true; } //JSON last error reset json_encode([]); return false; }
public function isValid($string) { if ($string !== false && $string !== null && $string !== '') { json_decode($string); if (json_last_error() === JSON_ERROR_NONE) { return true; } } return false; }
public static function validateJson($value, $params) { return (bool) (@json_decode($value)); }
final class Json extends AbstractRule { /** * {@inheritDoc} */ public function validate($input): bool { if (!is_string($input) || $input === '') { return false; } json_decode($input); return json_last_error() === JSON_ERROR_NONE; } }
final class Json extends AbstractRule { /** * {@inheritDoc} */ public function validate($input): bool { if (!is_string($input) || $input === '') { return false; } json_decode($input); return json_last_error() === JSON_ERROR_NONE; } }
public static function isJson($string) { json_decode($string); return json_last_error() == JSON_ERROR_NONE; }
function is_json( $argument, $ignore_scalars = true ) { if ( ! is_string( $argument ) || '' === $argument ) { return false; } if ( $ignore_scalars && ! in_array( $argument[0], [ '{', '[' ], true ) ) { return false; } json_decode( $argument, $assoc = true ); return json_last_error() === JSON_ERROR_NONE; }
if (\is_string($value)) { json_decode($value); //<------ HERE // Check if value is a valid JSON string. if ($value !== '' && json_last_error() !== JSON_ERROR_NONE) { /** * If the value is not empty and is not a valid JSON string, * it is most likely a custom field created in Joomla 3 and * the value is a string that contains the file name. */ if (is_file(JPATH_ROOT . '/' . $value)) { $value = '{"imagefile":"' . $value . '","alt_text":""}'; } else { $value = ''; } }
Stackoverflow questions related to this
In PHP, this question is one of the most high ranked questions related to json && php in stackoverflow, “Fastest way to check if a string is JSON in PHP?”. The question
Viewed 484k times. The ranking
Person asking how to do exactly this, also providing a real use case; eventhough in python, the programming language is not important. In Python
Someone has also doing exactly this , in JAVA. In Java
Open questions
Should we remove the capability of json_validate() to use the flag JSON_THROW_ON_ERROR? During the discussion in the inernals mailing list the user Rowan Tommins rowan.collins@gmail.com raised this concern.